|6502393||Hydraulic system with cross function regeneration||January, 2003||Stephenson et al.|
|6098647||Load-holding brake valve||August, 2000||Häussler et al.|
|5832807||Hydraulic control for a dividing machine tool||November, 1998||Rausch et al.||91/420|
|5611259||Hydraulic circuit for driving a ram of hydraulic press||March, 1997||Nagata||91/415|
|5191826||Hydraulic control device||March, 1993||Brunner|
|4624445||Lockout valve||November, 1986||Putnam||251/63.4|
|4423859||Impact damper||January, 1984||Müller|
|4319504||Damping device for abruptly occurring forces in a shear or shear press machine||March, 1982||Wepner et al.|
|4244275||Counterbalance valve||January, 1981||Smilges||91/420|
|4208935||Control system for a hydraulic press||June, 1980||Kollmar|
|4172582||Reverse differential holding valve||October, 1979||Bobnar||251/63|
|3906991||Hydraulic lowering check valve||September, 1975||Haussler||137/630.13|
|EP0464305||January, 1992||Hydraulic control device.|
|EP0765203||June, 1995||HYDRAULIC CONTROL SYSTEM FOR A CUTTING MACHINE TOOL|
|EP1186783||March, 2002||Hydraulic system with cross function regeneration|
|WO/1986/000849||February, 1986||PRESSURE-ADJUSTING SYSTEM FOR A HYDRAULICALLY-OPERATED CLUTCH AND/OR BRAKE FOR THE DRIVE SHAFT OF A PRESS|
|WO/1997/032136||September, 1997||LOAD-HOLDING BRAKE VALVE|
This application is a 371 national phase application of International Application No. PCT/DE03/01022 having an international filing date of Mar. 27, 2003, and which claims priority to German Application No. DE 102 23 267.9 filed May 24, 2002.
1. Field of the Invention
The invention relates to a hydraulic control in a hydraulic system for the operation of a machine tool such as a press for processing material of any desired type, such as presses and/or shears, in particular for shears for cutting metal scrap, such as “scrap shears”.
2. Prior Art
Machine tools such as presses essentially comprise
It is known to provide means in the hydraulic control which generate a damping pressure for damping a “(cutting) impact” at least in one of the hydraulic cylinders at the end of its working stroke, such as, for example, after the severing of metal scrap.
The general problematic nature of these (cutting) impacts has been known for a long time and has already been described in detail in publications DE 2808091A1, DE 2824176A1, DE 2909119A1, DE 3534467A1, DE 2221290C3, DE 2928777C2, DE 3112393C2 and DE 19529134A1.
A useful and already known solution to the problem can be gathered from the preamble of the main claim of EP 0765203B1 (also published as U.S. Pat. No. 5,832,807), in which case this embodiment is to be advantageously augmented by the characterizing features such as
The previously known hydraulic control can be effectively presented in the following steps with regard to the outflow relevant to the damping of the (cutting) impact (with reference to EP 0765203, also published as U.S. Pat. No. 5,832,807):
In addition, the (cutting) impact damping present per se is accordingly to be assisted with simple means by the 4th step, which, however, does not appear possible without further means or may lead to further complications.
The hydraulic controls already realized in industrial practice with the features (in accordance with the steps 1 to 3 described above) defined in the preamble of abovementioned EP 0765203B1 (also published as U.S. Pat. No. 5,832,807), in particular in scrap shears, have proved to be functional with regard to (cutting) impact damping; however, they are in need of improvement in the context of a complex hydraulic problem. With regard to the effectiveness of the technical means of the function described in step 4, this would only be partly realizable and only if additional means were to be used. This means at least a considerable cost outlay.
According to DE 4312283A1, the search for a solution approaches, such as, for example, in large, but continuously working channel baling presses, a control for a hydraulic heavy-duty actuator which is to be controlled under load from an extended working position into a return movement, a hydraulically pressurized working space of the actuator being connected to a return line of low pressure via a directional control valve, the valve position of which is set hydraulically via a control line which has at least one choke orifice.
In this case, a pressure-stabilizing delay element is connected in between the directional control valve and the choke orifice.
If the mode of operation of this control is analyzed with regard to the machine of the design mentioned at the beginning, valve operation for reducing relief impacts is certainly presented and a bracketed pressure from a system is reduced as smoothly as possible in order to reduce impacts extending into the tank line.
However, the rapid buildup of a counter-pressure in a cylinder and then also thus the limiting of this counter-pressure by this measure is not possible.
An approach to the solution of the present problem does not follow from this disclosure.
The aim of building up a counter-pressure as rapidly as possible and of limiting it in a cylinder of the machines of the generic type, taking into account their specific mode of operation, also cannot be achieved by the solution according to EP 1186783A1. According to this patent, only the oil flowing off from one cylinder is used for generally applying pressure to and driving a second cylinder. This effect is assumed to be known in order to actually fulfill the basic function of the hydraulic control in these machines.
It can therefore be stated that the problem of the (cutting) impact damping by means of hydraulic control for presses, and in particular shears for cutting metal scrap, defined at the beginning has hitherto not been solved comprehensively within the scope of the entire hydraulic system.
Thus, the volume of the hydraulic medium provided by the pumps in hydraulic controls for machine tools such as presses, and in particular shears for cutting metal scrap, constitutes a limit to the speed of the sequences of hydraulic cylinders, since the hydraulic medium flowing to the tank remains unused as a rule. There is also that fact that perpendicularly working hydraulic cylinders, such as in presses or shears, with attached masses of, for example, tools impose special demands on the hydraulic control. If the annular space of the cylinder is simply relieved toward the tank during the downward travel of this cylinder, the extension being effected downward, the piston of the cylinder could descend due to the dead mass and the attached load and could possibly run in advance of the action of the pumps. This has an adverse effect at least on the service life of the cylinder seals and may also be disadvantageous for the entire hydraulic system.
Finally, in conventional hydraulic controls for uses described above, with the simultaneous upward movement of two cylinders, the cycle time of the processing operation, such as after the shearing for example, is considerably restricted.
These problems, in their entirety, associated per se with the corresponding hydraulic system, such as
The object of the invention is to provide a hydraulic control in a hydraulic system for the operation of a machine tool such as a press for processing material of any desired type, in particular for scrap shears, which, in a functional combination of partly known features,
In effect, a complex hydraulic control in the hydraulic system for the operation of machine tools, such as presses, and in particular scrap shears, is provided which, in addition to the solved problem of functionally simple but functionally fully effective impact damping, increases the output rates of the material to be processed without increasing the installed capacity and the construction cost, whereby the operator can also be provided with a machine having a higher energy service value.
The invention is explained with reference to an exemplary embodiment according to the scheme of the hydraulic circuit for the operation of scrap shears with the aid of the drawings.
The circuit corresponding to the hydraulic system according to the invention is schematically shown in the drawing. In the drawing, the line _._. outlines the actual control.
In the drawing a first hydraulic cylinder 1.1 which drives a tool, such as a cutter slide with the cutter 1.1.3 which cuts material and a second hydraulic cylinder 1.2 which drives a further tool, such as a tamper 1.2.3 for holding down the material to be cut, are shown in a simplified manner. The cylinders 1.1 and 1.2 have bottom spaces 1.1.2 and 1.2.2, respectively and annular spaces 1.1.1 and 1.2.1, respectively. The hydraulic inlets or outlets for the hydraulic medium of the bottom spaces 1.1.2, 1.2.2 in both cylinders 1.1 and 1.2 are designated by A and the inlets and outlets for the hydraulic medium of the annular spaces 1.1.1, 1.2.1 are designated by B. T symbolizes the line to a tank or reservoir (not shown), and P1 and P2 symbolize the connections to the pressure lines and the pumps (not shown).
The basic circuit of the hydraulic control for the operation of the scrap shears is first of all preset with a second valve 2.2 between the bottom space 1.1.2 of the first hydraulic cylinder 1.1 and the tank or reservoir T and with a third valve 2.3 between the annular space 1.1.1 and the connection to the pressure supply P1.
Furthermore, a fifth valve 3.1 is provided between the bottom space 1.2.2 of the second hydraulic cylinder 1.2 and the connection to the pressure supply P2 and a sixth valve 3.2 is provided between the bottom space 1.2.2 and the tank or reservoir T.
Finally, a seventh valve 3.3 is arranged between the annular space 1.2.1 and the connection to the pressure supply P2 and an eighth valve 3.4 is arranged between the annular space 1.2.1 and the tank or reservoir T.
The function of the hydraulic control, which acts in the hydraulic system in accordance with the definition of the object, is explained in more detail in subsections I, II and III below.
I. Functional Part—(Cutting) Impact Damping
In scrap shears, the cutter slide 1.1.3 with the connected piston of the cylinder 1.1 is accelerated after the shearing of the material. The cause of the acceleration is a high pressure in the bottom space 1.1.2 of the cylinder 1.1 up to just before the cut occurs. The compressed volume of the hydraulic medium acts as an energy store. The compressed hydraulic medium accelerates the cylinder 1.1 with cutter slide 1.1.3. Before the cutting or shearing, the annular space 1.1.1 of the cylinder 1.1 is relieved. In order to counteract the acceleration of the cutter slide 1.1.3 and a resulting hydraulic impact, a counter-pressure is generated in the annular space 1.1.1 of the cylinder 1.1, this counter-pressure being suitable for damping the hydraulic impact.
At the instant directly before the material is cut through, a first valve 2.1 (not previously mentioned) between the bottom space 1.1.2 and the connection to pressure supply P1 and a pilot-control valve 2.4.3 (not previously mentioned) are in an operated position. As a result, the bottom space 1.1.2 of cylinder 1.1 is connected via the first valve 2.1 to the connection to the pressure supply P1, which is fed by hydraulic pumps (not shown). The annular space 1.1.1 of the first hydraulic cylinder 1.1 is relieved toward the tank (not shown) via a first main valve element 2.4.0 with a cap 2.4.1.
The drive motors (not shown) of the hydraulic pumps are protected against overload by a suitable output limit of the pumps. This output limit sets a lower delivery flow rate of the hydraulic medium at high pressures, so that the product of pressure and volumetric flow, which product corresponds to the hydraulic power, remains virtually constant. Accordingly, the volumetric flow rate of the hydraulic medium is low at high pressures compared with the volumetric flow rate at low pressures. The speed of the first hydraulic cylinder 1.1 is therefore also lower at high pressures compared with that at low pressures.
The opening stroke of the first main valve element 2.4.0 is adapted by an integrated spring (not designated) to the volumetric flow via the relevant valve.
During an abrupt rapid movement of the piston of the first hydraulic cylinder 1.1 (as described above), the first main valve 2.4.0 is delayed in its opening movement by a nozzle 18.104.22.168 essential to the invention. At the same time, the pressure in the annular space 1.1.1 of the cylinder 1.1 is set by the pressure valve 2.4.2, as pilot control of the first main valve element 2.4.0, to the pressure set at the pressure valve 2.4.2. The delay in the opening of the second main valve element 2.4.0 is surprisingly sufficient for generating a limited counter-pressure and thus for (cutting) impact damping.
Consequently, with simple means and in an advantageous manner, the maximum counter-pressure on the annular space side 1.1.1 of the first hydraulic cylinder 1.1 can be set higher than in the previously known solutions for generating a counter-pressure, whereby this partial solution can also be realized with less outlay in terms of construction.
II. Functional Part—Rapid-Motion Control Linked with Load Compensation
The delivery volume made available by the pumps has hitherto constituted a limit in the cylinder speed in hydraulic scrap shears, in which case the hydraulic medium flowing in a conventional manner to the tank is now to be utilized. Furthermore, perpendicularly working hydraulic cylinders 1.1 and 1.2 with attached loads due to the weight of the tools, such as cutter slide 1.1.3 and tamper 1.2.3, are to be controlled in a special manner.
If the annular spaces 1.1.1 and 1.2.1 were simply to be relieved toward the tank T during the downward travel of the cylinders 1.1 and 1.2, in the course of which the extension is effected downward, the respective piston of the hydraulic cylinders 1.1 and 1.2 could descend due to the dead weight caused by the attached load of said tools and could move in advance of the action of the hydraulic pumps. This would have adverse effects on the service life of the cylinder seals.
As a countermeasure during the downward travel in the respective annular space 1.1.1, 1.2.1, a pressure is to be generated which is large enough to compensate for the attached load, such as the tools for example. It has been determined in pilot tests that a pressure difference between annular spaces 1.1.1, 1.2.1 and bottom spaces 1.1.2 and 1.2.2 of the hydraulic cylinders 1.1, 1.2 is suitable for compensating for the load due to weight. At the same time, the hydraulic medium flowing off at B on the annular-space side is to be used for the purposes of a conventional rapid-motion control.
By means of the circuit according to the drawing, both requirements are realized in a combined manner by virtue of the fact that a second main valve element 2.7.0 with a cap 2.7.1, an intermediate plate 2.7.2, a pressure valve or choke (nozzle) 2.7.3 and a directional control valve 2.7.4 and, similarly, a third main valve element 3.7.0 with a cap 3.7.1, an intermediate plate 3.7.2, a pressure valve or choke (nozzle) 3.7.3 and a directional control valve 3.7.4 are arranged according to the invention.
These circuits are especially advantageous for downward movements with a low counterforce on the hydraulic cylinders 1.1, 1.2.
The respective valve combination, from the second and third main valve element 2.7.0, 3.7.0, interacts with a pilot-control arrangement which is formed by the cap 2.7.1, 3.7.1, intermediate plates 2.7.2, 3.7.2, pressure valves or chokes (nozzles) 2.7.3, 3.7.3 and the directional control valves 2.7.4, 3.7.4.
This pilot-control arrangement, in the linking according to the drawing, in combination with the respective main valve element 2.7.0, 3.7.0, constitutes a controllable pressure valve having a check function, in which case the pressure on the annular-space side can be set relative to the pressure on the piston side so as to be matched to the hydraulic cylinders 1.1, 1.2.
An alternative combination of a separate rapid-motion valve with load-compensation function could constitute an optimum solution from the energy point of view.
III. Functional Part—Transfer of the Hydraulic Medium
During the simultaneous upward movement of two cylinders 1.1, 1.2 as described above, the outflowing hydraulic medium of one of the cylinders 1.1, 1.2 is to be used for moving the other cylinder 1.1, 1.2. The quantity of hydraulic medium which is thus obtained compared with conventional concepts considerably reduces the cycle time of the press, and in particular of scrap shears, at the same pump delivery quantity.
The circuit according to the invention produces an increase in output compared with conventional concepts. The circuit for such use of the outflowing hydraulic medium is realized according to the invention by a fourth or switch valve 2.5 between the bottom space 1.2.2 of cylinder 1.2 and the annular space 1.1.1 of cylinder 1.1. In the circuit shown, the cylinders 1.1, 1.2 driven via the outflowing medium can be additionally driven with further pumps.
Although the invention is specifically explained with regard to the hydraulic system of scrap shears, it can be applied to the operation of machine tools such as presses of the generic type mentioned at the beginning in which, to all intents and purposes, the complex problem of impact damping, rapid-motion control with load compensation, and/or transfer of the hydraulic medium between at least two hydraulic cylinders is to be solved.